This application relates to methods for producing crystalline polycarbonate powders, and in particular to crystalline polycarbonate powders useful in additive manufacturing.
Additive manufacturing (AM), also known in the art as “three-dimensional” or “3D” printing, is a process for the manufacture of three-dimensional objects by formation of multiple fused layers.
AM methods that can be conducted using thermoplastic polymers such as polycarbonate include material extrusion (ME), for example fused deposition modelling, and powder bed fusing. In powder bed fusing thermal energy selectively fuses regions of a powder bed. In particular, selective laser sintering (SLS) is a powder bed fusion process using one or more lasers to fuse powdered thermoplastic polymers into the desired three-dimensional shape. Preferred powders for these processes have of a uniform shape, and size and composition. The preparation of such powders from thermoplastic polymers on an economic, large scale is not straightforward. In addition, It can be difficult to use amorphous polycarbonates, particularly in powder bed fusing processes such as SLS because they do not have a sharp melting point. This property causes the applied thermal energy source (e.g., a laser beam) to be dissipated into the regions surrounding where the energy beam strikes the bed. This undesired dissipation of thermal energy can cause unstable processing as well as poor feature resolution in the intended three-dimensional articles being produced. Preparation of crystalline polycarbonate having the desired particle sizes, particularly for powder bed fusion, is particularly difficult. Thus a need remains in the art for polycarbonate powder having good crystallinity and good particle size distribution.